Backlight dims on usage

Hello folks,

While watching DVD the backlight (media playing) becomes low after few minutes. I wish to know if there is some setting problem. Even the illuminated apple logo dims. Kindly help, thank you.

That's a built in "feature" Try Caffeine
Lighthead - Caffeine

Hi Ivan thanks for the link, will try it surely. Wish to add here that I have watched movies on macbook and the backlight has not gone low. But now its going dim in mere 4-5 minutes of playing DVD, its surprising ! Any clues??

try system preferences>energy saver
couple options there for screen dimming.